/**
 * floatObj 包含加减乘除四个方法，能确保浮点数运算不丢失精度
 */  
 
/*
 * 判断obj是否为一个整数
 */
    
function isInteger(obj) {        
  return Math.floor(obj) === obj    
}

    
/*
 * 将一个浮点数转成整数，返回整数和倍数。如 3.14 >> 314，倍数是 100
 * @param floatNum {number} 小数
 * @return {object}
 *   {times:100, num: 314}
 */
    
function toInteger(floatNum) {        
  var ret = {
    times: 1,
    num: 0
  }        
  if (isInteger(floatNum)) {            
    ret.num = floatNum            
    return ret        
  }        
  var strfi = floatNum + ''        
  var dotPos = strfi.indexOf('.');        
  var len = strfi.substr(dotPos + 1).length;        
  var times = Math.pow(10, len);        
  var intNum = parseInt(floatNum * times + 0.5, 10);        
  ret.times = times ;       
  ret.num = intNum        ;
  return ret    
}

    
/*
 * 核心方法，实现加减乘除运算，确保不丢失精度
 * 思路：把小数放大为整数（乘），进行算术运算，再缩小为小数（除）
 *
 * @param a {number} 运算数1
 * @param b {number} 运算数2
 * @param digits {number} 精度，保留的小数点数，比如 2, 即保留为两位小数
 * @param op {string} 运算类型，有加减乘除（add/subtract/multiply/divide）
 *
 */
    
function operation(a, b, digits, op) {        
  var o1 = toInteger(a)        
  var o2 = toInteger(b)        
  var n1 = o1.num        
  var n2 = o2.num        
  var t1 = o1.times        
  var t2 = o2.times        
  var max = t1 > t2 ? t1 : t2        
  var result = null        
  switch (op) {            
    case 'add':
                      if (t1 === t2) { // 两个小数位数相同
                            
        result = n1 + n2                
      } else if (t1 > t2) { // o1 小数位 大于 o2
                            
        result = n1 + n2 * (t1 / t2)                
      } else { // o1 小数位 小于 o2
                            
        result = n1 * (t2 / t1) + n2                
      }                
      return result / max            
    case 'subtract':
                      if (t1 === t2) {                    
        result = n1 - n2                
      } else if (t1 > t2) {                    
        result = n1 - n2 * (t1 / t2)                
      } else {                    
        result = n1 * (t2 / t1) - n2                
      }                
      return result / max            
    case 'multiply':
                      result = (n1 * n2) / (t1 * t2)                
      return result            
    case 'divide':
                      result = (n1 / n2) * (t2 / t1)                
      return result        
  }    
}

     // 加减乘除的四个接口
    
function add(a, b, digits) {        
  return operation(a, b, digits, 'add')    
}    
function subtract(a, b, digits) {        
  return operation(a, b, digits, 'subtract')    
}    
function multiply(a, b, digits) {        
  return operation(a, b, digits, 'multiply')    
}    
function divide(a, b, digits) {        
  return operation(a, b, digits, 'divide')    
}

function toFixed(num, s) {
  var times = Math.pow(10, s)
  var des = num * times + 0.5
  des = parseInt(des, 10) / times
  des = des + '';

  return changeDecimalBuZero(des,s);
} 
function formatDecimal(num, decimal) {
  num = num.toString()
  let index = num.indexOf('.')
  if (index !== -1) {
    num = num.substring(0, decimal + index + 1)
  } else {
    num = num.substring(0)
  }
  num = parseFloat(num)
  return toFixed(num, decimal)
}

function changeDecimalBuZero(number, bitNum) {
  /// <summary>
  /// 小数位不够，用0补足位数
  /// </summary>
  var f_x = parseFloat(number);
  if (isNaN(f_x)) {
    return 0;
  }
  var s_x = number.toString();
  var pos_decimal = s_x.indexOf('.');
  if (pos_decimal < 0) {
    pos_decimal = s_x.length;
    s_x += '.';
  }
  while (s_x.length <= pos_decimal + bitNum) {
    s_x += '0';
  }
  return s_x;
}

    // exports
module.exports = {        
  add: add,
  subtract: subtract,
  multiply: multiply,
  divide: divide,
  toFixed: toFixed,
  formatDecimal: formatDecimal
}